The invention provides a method and system for purifying a CO fuel gas through continuous pyrolysis of a carbon-containing organic matter. The system comprises a separation device, a breaking device, a rotary-bed pyrolyzing furnace, a fixed-bed pyrolyzing furnace, a condensing device, an oil-water separation device, a purifying device and a variable-pressure adsorption device. The method comprises the following steps: pretreating the carbon-containing organic matter and conveying to the rotary-bed pyrolyzing furnace for pyrolysis; treating the pyrolysis gas-liquid mixture obtained by the pyrolysis by the condensing device, the oil-water separation device and the gas purifying device to obtain a high-purity CO2 gas and combustible gases such as CH4, CO and H2; conveying the pyrolytic carbon obtained by the pyrolysis together with CO2 obtained by purifying the pyrolysis gas into a pyrolysis reactor of the fixed-bed pyrolyzing furnace for pyrolysis; and conveying the generated CO, alkane gases and the like together with the gases such as CO and H2 obtained by the pyrolysis of the rotary-bed pyrolyzing furnace and purification into the variable-pressure adsorption device to prepare the CO fuel gas. In the invention, large treatment quantity and low oil yield can be realized, the resources are saved, and industrial application is promoted.